1. Field of the Invention
This invention relates to sintered ferrite materials useful as various magnetic materials, and more particularly, to sintered ferrite materials which can be produced by sintering at relatively low temperatures. It also relates to chip parts using the same.
2. Prior Art
A variety of sintered ferrites have been used as various magnetic cores, magnetic shields, electromagnetic wave shields, attenuators and the like because of their magnetic properties. Among others, nickel base ferrites including Ni ferrites, Ni-Zn ferrites, and Ni-Cu-Zn ferrites have been widely used as low-temperature sinterable material to which printing and green sheet techniques are applicable.
These sintered ferrite materials are required to have a low sintering temperature, high density, high mechanical strength, and improved electromagnetic properties including magnetic permeability. Prior art ferrite materials, however, must be sintered at a very high temperature of at least about 1,100.degree. C. in order that they reach a sufficient density. High temperature heating undesirably increases the manufacturing expense. If the sintering temperature is not high enough, there results a sintered ferrite material having a commercially unsatisfactory level of density and mechanical strength as well as poor electromagnetic properties including magnetic permeability.
For example, chip inductors are often prepared by simultaneously sintering ferrite and electrode material, and silver is used as the electrode material. Sintering at a temperature in excess of 950.degree. C. would melt silver. This is a serious barrier to the manufacture of chip parts.
Japanese Patent Publication No. 62-29374 (published Jun. 25, 1987) discloses a magnetically soft material exhibiting a consistent, low temperature coefficient and having a spinel type ferrite composition consisting essentially of 45 to 64 mol % of ferric oxide, 10 to 50 mol % of nickel oxide, up to 40 mol % of zinc oxide, and 0.1 to 7 mol % of lithium oxide, said composition ranging from its stoichiometry to a composition having a 5 mol % short of ferric oxide. This material cannot be sintered at relatively low temperatures probably because of the absence of a tetravalent metal oxide requisite to the present invention as will be described below.